Methionine Pool Research Articles

Selective Methionine Pool Exhaustion Mediated by a Sequential Positioned MOF Nanotransformer for Intense Cancer Immunotherapy.

Cancer cells are addictive to exogenous methionine to gear toward tumor proliferation. Meanwhile, they could replenish methionine pool from polyamine metabolism through methionine salvage pathway. However, the current developed therapeutic tactics for methionine depletion remain facing great challenges in terms of the selectivity, safety and efficiency. Herein, a sequential positioned metal organic framework (MOF) nanotransformer was designed to selectively exhaust methionine pool via inhibiting the uptake of methionine and throttling its salvage pathway for enhanced cancer immunotherapy. The MOF nanotransformer could restrain the open source and reduce the reflux of methionine to exhaust methionine pool of cancer cells. Moreover, the intracellular traffic routes of sequential positioned MOF nanotransformer matched well with the distribution of polyamines, which was conducive to the oxidation of polyamines via its responsive deformability and nanozyme-augmented Fenton-like reaction for the final exhaustion of intracellular methionine. Our results verified that the well-designed platform could not only kill cancer cells efficiently but also promote the infiltration of CD8 and CD4 T cells for intensive cancer immunotherapy. Overall, we believe that our work will inspire the construction of novel MOF-based antineoplastic platform and provide new insights into the development of metabolic-related immunotherapy. This article is protected by copyright. All rights reserved.

Abstract 3093: Synthesis and bioevaluation of LAT-1 efflux agonists for the treatment of pancreatic cancers

Abstract The purpose of this report is to describe the discovery and development of the world’s first L-type amino acid transporter 1 (LAT-1) efflux agonist. LAT-1 is used for the import of amino acid substrates (leucine, phenylalanine, and methionine) and LAT-1 expression has been showed to be increased in pancreatic ductal adenocarcinoma (PDAC) cells. LAT-1 is a promising target for the treatment of rapidly growing cancers, such as PDAC, in part, due to its key role in methionine import. Methionine is required for various cellular processes, including the generation of S-adenosylmethionine (SAM) and the maintenance of intracellular polyamine pools, which are essential for PDAC growth. Indeed, the biosynthesis of the higher polyamines (spermidine and spermine) requires the transfer of an aminopropyl group from decarboxylated S-adenosylmethionine (dc-SAM), illustrating the molecular connection between methionine and polyamine pools. LAT-1 inhibition, such as with the known LAT-1 inhibitor JPH203, has shown efficacy in suppressing tumor growth in pancreatic cancer cell lines. While the early pre-clinical data is promising, competitive inhibitors of LAT-1 may have limited potency in the presence of high extracellular levels of LAT-1 substrates. In contrast, LAT-1 efflux agonists are insensitive to extracellular LAT-1 substrates. These novel compounds reverse the flow of substrates through LAT-1, effectively depleting cells of key intracellular amino acids, rather than blocking the import of extracellular substrates like methionine. The chiral piperazine (1), our lead efflux agonist, was discovered by a high throughput screen and was shown to deplete intracellular methionine, leucine and phenylalanine pools by LC-MS as well as decrease the synthesis of the higher polyamines (spermidine and spermine), a process which is reliant upon methionine as a precursor. A structure activity relationship (SAR) analysis of the four possible diastereomers of 1 was performed. The performance of these diastereomers and other derivatives were evaluated by LC-MS, HPLC, and Western blot. These molecules were shown to increase 3H-leucine efflux, decrease intracellular polyamine, SAM, and S-adenosylhomocysteine (SAH) levels, decrease phosphatidylethanolamine levels and induce the autophagic marker LC3-II. In summary, this novel method of methionine restriction allows one to alter intracellular methionine levels in a dose-dependent manner and provides a novel way to control pancreatic cancer cell growth. Citation Format: Holly Moots, Houssine Ikhlef, Vandana Sekhar, Otto Phanstiel. Synthesis and bioevaluation of LAT-1 efflux agonists for the treatment of pancreatic cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3093.

An ethylene‐hypersensitive methionine sulfoxide reductase regulated by NAC transcription factors increases methionine pool size and ethylene production during kiwifruit ripening

Ethylene plays an important role in regulating fruit ripening by triggering dynamic changes in expression of ripening-associated genes, but the functions of many of these genes are still unknown. Here, a methionine sulfoxide reductase gene (AdMsrB1) was identified by transcriptomics-based analysis as the gene most responsive to ethylene treatment in ripening kiwifruit. The AdMsrB1 protein exhibits a stereospecific activity toward the oxidative stress-induced R enantiomer of methionine sulfoxide (MetSO), reducing it to methionine (Met). Stable overexpression of AdMsrB1 in kiwifruit significantly increased the content of free Met and 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, and increased ethylene production. Dual-luciferase assays indicated that the AdMsrB1 promoter was not directly upregulated by ethylene treatment but was modulated by two ethylene-inducible NAM/ATAF/CUC transcription factors (AdNAC2 and AdNAC72) that bind directly to the AdMsrB1 promoter. Overexpression of AdNAC72 in kiwifruit not only enhanced AdMsrB1 expression, but also increased free Met and ACC content and ethylene production rates. This finding establishes an unexpected regulatory loop that enhances ethylene production and the concentration of its biosynthetic intermediates.

Disulfiram Inhibits M. tuberculosis Growth by Altering Methionine Pool, Redox Status and Host-Immune Response

Methionine biosynthetic pathway, essential for the growth of Mycobacterium tuberculosis (Mtb) in the host, represents an attractive target for the development of novel anti-tuberculars. Here, we have biochemically characterized homoserine acetyl transferase (HSAT viz. MetA) of Mtb, which catalyses the first committed step of methionine and S-adenosylmethionine (SAM) biosynthesis. High-throughput screening of a 2300 compound library resulted in identification of thiram, an anti-fungal organosulfur compound, as the most potent MetA inhibitor. Further analysis of thiram analogs led to the identification of orally bioavailable disulfiram (DIS, an anti-alcoholism FDA approved drug) as a novel inhibitor of MetA. Both thiram and DIS restricted the growth of drug-sensitive and drug-resistant Mtb strains in a bactericidal manner. ThermoFlour assay demonstrated direct binding of DIS with MetA. Metabolomic and transcriptomic studies showed DIS mediated perturbation of methionine and redox homeostasis, respectively, in Mtb. In concordance, the effect of DIS on Mtb growth was partially rescued by supplementation with either L-methionine as well as N-acetyl cysteine, suggesting a multi-target killing mechanism. In Mtb-infected mice, DIS administration restricted bacterial growth, increased efficacy of isoniazid, ameliorated lung pathology, modulated lung immune cell landscape and protective immune response. Taken together, our results demonstrate that DIS can be repurposed for designing an effective anti-tubercular therapy. Funding Statement: The research fellowship to D.C. and T.P.G. from Department of Biotechnology, Govt. of India is acknowledged. Ava.S. fellowship was supported by the University of Grants commission. R.B. acknowledges Department of Science and Technology India and FICCI for providing C.V. Raman International fellowship. R.S. acknowledge THSTI, and Department of Biotechnology, Govt. of India (BT/PR29075/BRB/10/1699/2018) for funding. This research was supported by SIgN A*STAR, A*STAR JCO-CDA grant (#1518251030), and Singapore-India Joint grant (#1518224018) to A.S. Declaration of Interests: None. Ethics Approval Statement: The proposed animal experiments were approved by the institutional animal ethics committee of Defence Science Organization (DSO), Singapore.

The Key Role of Purine Metabolism in the Folate-Dependent Phenotype of Autism Spectrum Disorders: An In Silico Analysis.

Folate deficiency in the critical developmental period has been repeatedly associated with an increased risk of Autism spectrum disorders (ASD), but the key pathophysiological mechanism has not yet been identified. In this work, we focused on identifying genes whose defect has similar consequences to folate depletion in the metabolic network. Within the Flux Balance Analysis (FBA) framework, we developed a method of blocked metabolites that allowed us to define the metabolic consequences of various gene defects and folate depletion. We identified six genes (GART, PFAS, PPAT, PAICS, ATIC, and ADSL) whose blocking results in nearly the same effect in the metabolic network as folate depletion. All of these genes form the purine biosynthetic pathway. We found that, just like folate depletion, the blockade of any of the six genes mentioned above results in a blockage of purine metabolism. We hypothesize that this can lead to decreased adenosine triphosphate (ATP) and subsequently, an S-adenosyl methionine (SAM) pool in neurons in the case of rapid cell division. Based on our results, we consider the methylation defect to be a potential cause of ASD, due to the depletion of purine, and consequently S-adenosyl methionine (SAM), biosynthesis.

Involvement of proinflammatory cytokines and metallothionein in the repairing of arsenic-mediated uterine tissue damage by curcumin.

Background Curcumin is extensively used as a therapeutic intervention for treating several ailments. The antioxidant curcumin has an anti-inflammatory and chelating property with arsenic to exhibit a strong therapeutic effect on reproductive organs. This study was undertaken to describe the protective effect of noninvasive administration of curcumin against sodium-arsenite-mediated uterine hazards in female Wistar rats. Methods Twenty-four female Wistar rats were randomly divided into four groups. The treatment was continued for 8 days and given orally sodium arsenite (10 mg/kg body weight) in combination with curcumin (20 mg/kg body weight). Results Our evaluation revealed that 8 days of sodium arsenite (10 mg/kg body weight) treatment reduced the activities of the uterine enzymatic antioxidants superoxide dismutase, catalase, and peroxidase. Blood levels of vitamin B12 and folic acid decreased followed by an increased serum lactate dehydrogenase, homocysteine level, and hepatic metallothionein-1 in arsenic-treated rats. Necrosis of uterine tissue along with the disruption of ovarian steroidogenesis was marked in arsenic-treated rats with an upregulation of uterine NF-κB and IL-6 along with a raised level of serum TNF-α. Oral administration of curcumin (20 mg/kg body weight/day) in arsenic-treated rats significantly reinstated these alterations of the antioxidant system followed by an improvement of ovarian steroidogenesis and the circulating level of B12 and folate along with the downregulation of serum homocysteine, metallothionein-1, and cytokines. Conclusions The findings of this study clearly and strongly elucidated that arsenic-induced oxidative stress in uterus is linked to an alteration of inflammation-signaling biomarkers and these have been protected through the co-administration of curcumin due to its anti-inflammatory, free radical scavenging, and antioxidant activity by the possible regulation of an S-adenosine methionine pool.

Dietary CCPS from bitter gourd attenuates sodium arsenite induced female reproductive ailments cum infertility in wistar rats: anti-inflammatory and anti-apoptotic role

This investigation explored a dietary therapy of pectic polysaccharide (CCPS) (2 mg/ Kg BW) against female repro-toxicity and infertility triggered by sodium arsenite (As3+) (10 mg/ Kg BW) in Wistar rats. The isolated CCPS consists of D-galactose and D-methyl galacturonate with a molar ratio of 1: 4. FTIR spectral analysis of CCPS and CCPS- sodium arsenite (As3+) complex indicated a possible chelating property of CCPS in presence of binding sites (OH−/COOH) for As3+. Series of negatively charged galacturonate residues in CCPS provide better potential for cation chelation. CCPS significantly mitigated As3+ induced ovarian, uterine lipid peroxidation, and reactive oxygen species (ROS) generation by the restoration of superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) activities. CCPS post-treatment enhanced ovarian steroidogenesis along with a restoration of normal tissue histoarchitecture in As3+ fed rats by regulating the estradiol receptor alpha (ER-α). CCPS suppressed anti-inflammatory properties effectively found since a down-regulation of NF-kappa B (NF-қB), pro-inflammatory tumor necrosis-α (TNF-α) and interleukin-6 (IL-6) were observed in arsenicated rats with CCPS. This study confirmed the up-regulation of uterine pro-apoptotic/ apoptotic proteins caspase-3, poly ADP ribose polymerase (PARP), proliferating cell nuclear antigen (PCNA), phospho p53 and Bax, followed by down-regulation of Bcl-2 and protein Kinase B (AKT) signaling pathway along with uterine tissue regeneration in As3+ exposed rats. Oral CCPS attenuated the above apoptotic expressional changes significantly and dietary CCPS ensured successful fertility with the birth of healthy pups in lieu of infertile condition in As3+ fed rats. Moreover, this study also supports that CCPS treatment attenuated the As3+ toxicity by modulating the S-adenosine methionine (SAM) pool components, B12, folate and homocysteine.

Involvement of metallothionein, homocysteine and B-vitamins in the attenuation of arsenic-induced uterine disorders in response to the oral application of hydro-ethanolic extract of Moringa oleifera seed: a preliminary study

The painful invasive chelation therapy makes it challenging to continue the prolonged treatment against arsenic toxicity. Hence, the significance of the present preliminary investigation was to explore a noninvasive treatment strategy against sodium arsenite (As3+) by the use of a hydroethanolic extract of Moringa oleifera (MO) seed. Arsenic treatment (10 mg/kg body-weight) in animals showed significant level of oxidative stress as evidenced by increased serum levels of malondialdehyde (MDA), conjugated dienes (CD) and reduced level of non-protein thiol (NPSH). A significant diminution in the activities of enzymatic antioxidants was noted in As3+-treated rats. As3+ treatment showed a lengthy phase of metestrous in animals followed by significantly diminished ovarian steroidogenesis, increased ovarian follicular degeneration and distortion of uterine tissue histomorphology. In addition, there was a significant depletion of Vitamin-B9 (folate) and B12 following As3+ ingestion. The levels of circulating TNF-α, homocysteine (Hcy), uterine-IL-6, and liver metallothionein (MT-1) were significantly elevated in arsenic treated rats. MO at a dose of 100 mg/kg body-weight could successfully mitigate the uterine ROS generation by maintaining the uterine antioxidant status in As3+- treated rats. This seed extract prevented the deterioration of As3+-mediated ovarian-steroidogenesis and ovarian and uterine histoarchitecture significantly. B9 and B12 levels were also improved following the ingestion of the MO extract in arsenicated animals. Elevation of Hcy, TNF-α and IL-6 was also prevented by this MO seed extract in As3+-treated rats. A further increase of MT-1 level was achieved after MO ingestion in As3+-treated rats. Here, the alleviation of arsenic toxicity might involve via the regulation of the components of S-adenosine methionine (SAM) pool and MT-1.

Engineering sulfur storage in maize seed proteins without apparent yield loss

Sulfur assimilation may limit the pool of methionine and cysteine available for incorporation into zeins, the major seed storage proteins in maize. This hypothesis was tested by producing transgenic maize with deregulated sulfate reduction capacity achieved through leaf-specific expression of the Escherichia coli enzyme 3'-phosphoadenosine-5'-phosphosulfate reductase (EcPAPR) that resulted in higher methionine accumulation in seeds. The transgenic kernels have higher expression of the methionine-rich 10-kDa δ-zein and total protein sulfur without reduction of other zeins. This overall increase in the expression of the S-rich zeins describes a facet of regulation of these proteins under enhanced sulfur assimilation. Transgenic line PE5 accumulates 57.6% more kernel methionine than the high-methionine inbred line B101. In feeding trials with chicks, PE5 maize promotes significant weight gain compared with nontransgenic kernels. Therefore, increased source strength can improve the nutritional value of maize without apparent yield loss and may significantly reduce the cost of feed supplementation.

Arjunolic Acid Improves the Serum Level of Vitamin B12 and Folate in the Process of the Attenuation of Arsenic Induced Uterine Oxidative Stress.

Continuation of prolonged treatment against arsenicosis with conventional chelating therapy is a global challenge. The present study was intended to evaluate the defensive effect of arjunolic acid against arsenic-induced oxidative stress and female reproductive dysfunction. Wistar strain adult female rats were given sodium arsenite (10mg/kg body weight) in combination with arjunolic acid (10mg/kg body weight) orally for two estrous cycles. Electrozymographic analysis explored that arjunolic acid co-treatment counteracted As3+-induced ROS production in uterine tissue by stimulating the activities of endogenous enzymatic antioxidants. Arjunolic acid was able to enhance the protection against mutagenic uterine DNA breakage, necrosis, and ovarian-uterine tissue damages in arsenicated rats by improving the ovarian steroidogenesis. The mechanisms might be coupled with the augmentation of antioxidant defense system, partly through the elimination of arsenic with the involvement of S-adenosyl methionine pool where circulating levels of vitamin B12, folic acid, and homocysteine play critical roles as evidenced from our present investigation.

Structural Snapshots of an Engineered Cystathionine-γ-lyase Reveal the Critical Role of Electrostatic Interactions in the Active Site.

Enzyme therapeutics that can degrade l-methionine (l-Met) are of great interest as numerous malignancies are exquisitely sensitive to l-Met depletion. To exhaust the pool of methionine in human serum, we previously engineered an l-Met-degrading enzyme based on the human cystathionine-γ-lyase scaffold (hCGL-NLV) to circumvent immunogenicity and stability issues observed in the preclinical application of bacterially derived methionine-γ-lyases. To gain further insights into the structure-activity relationships governing the chemistry of the hCGL-NLV lead molecule, we undertook a biophysical characterization campaign that captured crystal structures (2.2 Å) of hCGL-NLV with distinct reaction intermediates, including internal aldimine, substrate-bound, gem-diamine, and external aldimine forms. Curiously, an alternate form of hCGL-NLV that crystallized under higher-salt conditions revealed a locally unfolded active site, correlating with inhibition of activity as a function of ionic strength. Subsequent mutational and kinetic experiments pinpointed that a salt bridge between the phosphate of the essential cofactor pyridoxal 5'-phosphate (PLP) and residue R62 plays an important role in catalyzing β- and γ-eliminations. Our study suggests that solvent ions such as NaCl disrupt electrostatic interactions between R62 and PLP, decreasing catalytic efficiency.

The Allosteric Regulatory Mechanism of the E.Coli Metni Methionine ABC Transporter

The MetNI methionine importer of Escherichia coli, an ATP Binding Cassette (ABC) transporter, uses the energy of ATP binding and hydrolysis to catalyze the high affinity uptake of D- and L-methionine. Early in vivo studies showed that the uptake of external methionine is repressed by the level of the internal methionine pool, a phenomenon termed transinhibition. Our understanding of MetNI mechanism has thus far been limited to a series of crystal structures in an inward facing conformation. To understand the molecular mechanism of transinhibition, we studied the kinetics of ATP hydrolysis using detergent-solubilized MetNI. We find that transinhibition is due to noncompetitive inhibition by L-methionine, much like a negative feedback loop. Thermodynamic analyses revealed two allosteric methionine binding sites per transporter. This quantitative analysis of transinhibition, the first to our knowledge for a structurally defined transporter, builds upon the previously proposed structurally based model for regulation. This mechanism of regulation at the transporter activity level could be applicable to not only ABC transporters but other types of membrane transporters as well.

The Allosteric Regulatory Mechanism of the Escherichia coli MetNI Methionine ATP Binding Cassette (ABC) Transporter

The MetNI methionine importer of Escherichia coli, an ATP binding cassette (ABC) transporter, uses the energy of ATP binding and hydrolysis to catalyze the high affinity uptake of D- and L-methionine. Early in vivo studies showed that the uptake of external methionine is repressed by the level of the internal methionine pool, a phenomenon termed transinhibition. Our understanding of the MetNI mechanism has thus far been limited to a series of crystal structures in an inward-facing conformation. To understand the molecular mechanism of transinhibition, we studied the kinetics of ATP hydrolysis using detergent-solubilized MetNI. We find that transinhibition is due to noncompetitive inhibition by L-methionine, much like a negative feedback loop. Thermodynamic analyses revealed two allosteric methionine binding sites per transporter. This quantitative analysis of transinhibition, the first to our knowledge for a structurally defined transporter, builds upon the previously proposed structurally based model for regulation. This mechanism of regulation at the transporter activity level could be applicable to not only ABC transporters but other types of membrane transporters as well.

Selenomethionine and Total Methionine Ratio is Conserved in Seed Proteins of Selenium‐Treated and Nontreated Soybean, Flax, and Potato

ABSTRACTCrop biofortification with Se is widely accepted. However, little is known about the efficiency of selenomethionine (Se‐Met) incorporation into the seed and tuber protein fraction of crops. Here, we report on the efficiency of Se incorporation into the seed and tuber protein fraction of soybean, flax, and potato and the putative identity of some of the proteins that are likely targets for this random pretranslation modification. Soybean, flax, and potato plants received Se using different sodium selenate application methods and rates, and Se‐Met was determined in seed, tuber, and their protein fractions. Selenium content in seed and tuber tissues and in protein fractions was increased by 2 to 86 times. The methionine (Met) pool was increased, as was the proportion of Se‐Met in the Met pool, but the ratio of Se‐Met:total Met was well conserved (1:1) between the treated and nontreated plants. After two‐dimensional (2D) protein electrophoresis, five protein spots were identified as glycinin, trypsin inhibitor (soybean), patatin‐3‐Kuras‐1, patain‐B2, and phosphoenol carboxy kinase (potato), none of which showed S to Se substitution in their primary structure. Linking Se and three stress markers in fresh tuber extracts, glutathione (GSH) level, glutathione peroxidase (GPx), and glutathione reductase (GR) activities were increased by 20 to 35%. The data showed low protein modification in these non‐Se‐accumulator crops and indicated that rates of 5 to 10 g ha–1 Se, through foliar application, may ensure not only an adequate daily intake levels for humans but may also activate antioxidant enzyme systems within the tuber tissue.

Folate Pathway Disruption Leads to Critical Disruption of Methionine Derivatives in Mycobacterium tuberculosis

In this study, we identified antifolates with potent, targeted activity against whole-cell Mycobacterium tuberculosis (MTB). Liquid chromatography-mass spectrometry analysis of antifolate-treated cultures revealed metabolic disruption, including decreased pools of methionine and S-adenosylmethionine. Transcriptomic analysis highlighted altered regulation of genes involved in the biosynthesis and utilization of these two compounds. Supplementation with amino acids or S-adenosylmethionine was sufficient to rescue cultures from antifolate treatment. Instead of the "thymineless death" that characterizes folate pathway inhibition in a wide variety of organisms, these data suggest that MTB is vulnerable to a critical disruption of the reactions centered around S-adenosylmethionione, the activated methyl cycle.

Biosynthesis of poly(4-hydroxybutyrate) in recombinant Escherichia coli grown on glycerol is stimulated by propionic acid

One of the most promising polyhydroxyalkanoates (PHAs) for medical applications is poly(4-hydroxybutyrate) (P4HB) due to its biodegradability, biocompatibility and mechanical properties. Currently, the major hurdle for expanding P4HB applications is the production and recovery cost. In this study, we investigated the stimulating factors for P4HB biosynthesis with the ultimate goal of reducing production cost. We found that addition of propionic acid to the culture medium stimulates the P4HB accumulation in recombinant Escherichia coli JM109 grown on glycerol. This stimulating effect was significantly weakened by addition of exogenous methionine, whereas it was not influenced by addition of cysteine. These results suggest that propionic acid enhances P4HB synthesis by reducing the intracellular methionine pool. Utilizing these findings for P4HB production in batch cultures on glycerol, the volumetric yield of P4HB could be improved 4 fold from 0.9g/L to 3.7g/L by adding 2g/L propionic acid into the medium.

Quantitation of Cellular Metabolic Fluxes of Methionine

Methionine is an essential proteogenic amino acid. In addition, it is a methyl donor for DNA and protein methylation and a propylamine donor for polyamine biosynthesis. Both the methyl and propylamine donation pathways involve metabolic cycles, and methods are needed to quantitate these cycles. Here, we describe an analytical approach for quantifying methionine metabolic fluxes that accounts for the mixing of intracellular and extracellular methionine pools. We observe that such mixing prevents isotope tracing experiments from reaching the steady state due to the large size of the media pools and hence precludes the use of standard stationary metabolic flux analysis. Our approach is based on feeding cells with (13)C methionine and measuring the isotope-labeling kinetics of both intracellular and extracellular methionine by liquid chromatography-mass spectrometry (LC-MS). We apply this method to quantify methionine metabolism in a human fibrosarcoma cell line and study how methionine salvage pathway enzyme methylthioadenosine phosphorylase (MTAP), frequently deleted in cancer, affects methionine metabolism. We find that both transmethylation and propylamine transfer fluxes amount to roughly 15% of the net methionine uptake, with no major changes due to MTAP deletion. Our method further enables the quantification of flux through the pro-tumorigenic enzyme ornithine decarboxylase, and this flux increases 2-fold following MTAP deletion. The analytical approach used to quantify methionine metabolic fluxes is applicable for other metabolic systems affected by mixing of intracellular and extracellular metabolite pools.

Towards methionine overproduction in Corynebacterium glutamicum - methanethiol and dimethyldisulfide as reduced sulfur sources

In the present work, methanethiol and dimethyldisulfide were investigated as sulfur source for methionine synthesis in Corynebacterium glutamicum. In silico pathway analysis has predicted a high methionine yield for these reduced compounds provided that they can be utilized. Wild type cells were able to grow on methanethiol and on dimethyldisulfide as sole sulfur source, respectively. Isotope labeling studies with mutant strains exhibiting targeted modification of methionine biosynthesis gave detailed insight into the underlying pathways involved in assimilation of methanethiol and dimethyldisulfide. Both sulfur compounds are incorporated as entire molecule, adding the terminal S-CH3 group to O-acetylhomoserine. In this reaction, methionine is directly formed. MetY (O-acetylhomoserine sulfhydrylase) was identified as enzyme catalyzing this reaction. Deletion of metY resulted in methionine auxotrophic strains grown on methanethiol or dimethyldisulfide as sole sulfur source. Plasmid based overexpression of metY in the delta metY background restored the capability to grow on methanethiol or dimethyldisulfide as sole sulfur source. In vitro studies with the C. glutamicum wild type revealed a relatively low activity of MetY for methanethiol (63 mU/mg) and dimethyldisulfide (61 mU/mg). Overexpression of metY increased the in vitro activity to 1780 mU/mg and was beneficial for methionine production, since the intracellular methionine pool was increased two-fold in the engineered strain. This positive effect was limited by depletion of the metY substrate O-acetylhomoserine, requesting for further metabolic engineering targets towards competitive production strains.

In Vivo Residue-specific Histone Methylation Dynamics

Methylation of specific histone residues is capable of both gene activation and silencing. Despite vast work on the function of methylation, most studies either present a static snapshot of methylation or fail to assign kinetic information to specific residues. Using liquid chromatography-tandem mass spectrometry on a high-resolution mass spectrometer and heavy methyl-SILAC labeling, we studied site-specific histone lysine and arginine methylation dynamics. The detection of labeled intermediates within a methylation state revealed that mono-, di-, and trimethylated residues generally have progressively slower rates of formation. Furthermore, methylations associated with active genes have faster rates than methylations associated with silent genes. Finally, the presence of both an active and silencing mark on the same peptide results in a slower rate of methylation than the presence of either mark alone. Here we show that quantitative proteomic approaches such as this can determine the dynamics of multiple methylated residues, an understudied portion of histone biology.

Effect of Se source and dose on selenomethionine and selenocysteine levels in blood and plasma of mature horses

The study comprised 25 mature horses and incorporated five dietary treatments; a nega tive control (C: 0.085 mg Se/kg DM), 3 levels of Se yeast supplementation, obtained from Saccharomyces cerevisiae CNCM I-3060 (OS2, OS3 and OS4: 0.2, 0.3 and 0.4 mg Se/kg DM respectively) and one positive control supplemented with Na selenite (IS3: 0.3 mg Se/kg DM). Diets were offered for 112 days. Total Se, proportion of total Se comprised as selenomethionine (SeMet) or selenocysteine (SeCys) of pooled samples of blood and plasma for each treatment at d 0.56 and 112 were determined. Total Se and SeCys increased both in blood and plasma during the trial in all treatments supplemented with Se; these increases were proportional to the level of dietary Se supplementation. The SeMet increased only in treatments supplemented with Se yeast, with increases proportional to the level of dietary Se supplementation. In Se yeast horses the proportion of total Se comprised as SeMet accounted for 20 and 14% of total Se increase in blood and plasma respectively; in IS3 only accounted for 5 and 3% respectively. These results seem support the view that SeMet is a non-specific form of Se that is metabolized as a constituent of the methionine pool, and can be considered as a storage form of Se in higher animals.